1. Field of Invention
The present invention is related to a touch panel, and more specifically, to a touch panel that determines the capacitance of a panel capacitor thereof based on the operations of three pairs of switches.
2. Description of Related Art
With the rapid development of technology, most electronic devices, such as notebook computers, mobile phones or portable multimedia players, usually have touch panels serving as input interfaces of a new generation in replacement of conventional keyboards. The touch panels are generally classified into capacitive and resistive touch panels. The capacitive touch panels are operated by approaching or touching the touch panels with a finger or a conductive material to change the capacitances of the touch panels. While variations in the capacitances are detected, the location approached or touched by the finger or the conductive material is determined, and an operation corresponding to the approached or touched location is performed.
FIG. 1 is a functional block diagram of a conventional touch panel 14 according to the related art. The touch panel 14 has a unit under test (UUT) 16 and an analog to digital converter (ADC) 18. The information of the capacitance of the UUT 16 is delivered to the ADC 18, such that the ADC 18 converts the capacitance of the UUT 16 into a digital form. The range of the capacitance of the UUT 16 is 0 to 50 pF (picofarad), and the ADC is a 16-bits converter. It is assumed that the capacitance of the UUT 16 is 25 pF when the UUT 16 is not touched, and that the capacitance of the UUT 16 is 25.1 pF when the UUT 16 is touched. In other words, the capacitance of the UUT 16 is changed from 25 pF to 25.1 pF, and the values of the corresponding digital codes outputted from ADC 18 are 32768 (i.e.
      2    16    ×      25    50  ) and 32899 (i.e.)
      2    16    ×      25.1    50  ) respectively. The difference between the values of the two digital codes is 131, which corresponds to the capacitance difference of 0.1 pF. It could be seen that the ADC 18 always converts the untouched capacitance of the UUT 16 (i.e. 25 pF) even if the capacitance difference of the UUT 16 is small, such that the ADC 18 always operates with high energy consumption.